diff --git a/CHANGELOG.md b/CHANGELOG.md
index d976ad4b9..41266d5f0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -9,6 +9,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Added
 
+- Add `GlobalDummyDatastore` to support testing and development of global domain models without requiring large datasets. [\#453](https://github.com/mllam/neural-lam/pull/453) @sohampatil01-svg
+
 - Enable `pin_memory` in DataLoaders when GPU is available for faster async CPU-to-GPU data transfers [\#236](https://github.com/mllam/neural-lam/pull/236) @abhaygoudannavar
 
 ### Changed
diff --git a/neural_lam/models/ar_model.py b/neural_lam/models/ar_model.py
index f1bcb461d..e8f7ca8eb 100644
--- a/neural_lam/models/ar_model.py
+++ b/neural_lam/models/ar_model.py
@@ -327,7 +327,10 @@ def all_gather_cat(self, tensor_to_gather):
 
         returns: (K*d1, d2, ...)
         """
-        return self.all_gather(tensor_to_gather).flatten(0, 1)
+        gathered = self.all_gather(tensor_to_gather)
+        if gathered.dim() > tensor_to_gather.dim():
+            return gathered.flatten(0, 1)
+        return gathered
 
     # newer lightning versions requires batch_idx argument, even if unused
     # pylint: disable-next=unused-argument
diff --git a/tests/conftest.py b/tests/conftest.py
index 47237ed55..c3f6a1445 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -16,7 +16,7 @@
 )
 
 # Local
-from .dummy_datastore import DummyDatastore
+from .dummy_datastore import DummyDatastore, GlobalDummyDatastore
 
 # Disable weights and biases to avoid unnecessary logging
 # and to avoid having to deal with authentication
@@ -103,9 +103,11 @@ def download_meps_example_reduced_dataset():
     ),
     npyfilesmeps=None,
     dummydata=None,
+    dummydata_global=None,
 )
 
 DATASTORES[DummyDatastore.SHORT_NAME] = DummyDatastore
+DATASTORES[GlobalDummyDatastore.SHORT_NAME] = GlobalDummyDatastore
 
 
 def init_datastore_example(datastore_kind):
diff --git a/tests/dummy_datastore.py b/tests/dummy_datastore.py
index e3de83ca4..3108bb0cd 100644
--- a/tests/dummy_datastore.py
+++ b/tests/dummy_datastore.py
@@ -466,3 +466,18 @@ def grid_shape_state(self) -> CartesianGridShape:
 
         n_points_1d = int(np.sqrt(self.num_grid_points))
         return CartesianGridShape(x=n_points_1d, y=n_points_1d)
+
+
+class GlobalDummyDatastore(DummyDatastore):
+    """
+    Dummy datastore that represents a global domain (no lateral boundaries).
+    """
+
+    SHORT_NAME = "dummydata_global"
+
+    @cached_property
+    def boundary_mask(self) -> xr.DataArray:
+        """
+        Return an all-zero boundary mask.
+        """
+        return xr.zeros_like(self.ds["boundary_mask"])
diff --git a/tests/test_datastores.py b/tests/test_datastores.py
index c719c69df..885d8f2a8 100644
--- a/tests/test_datastores.py
+++ b/tests/test_datastores.py
@@ -229,9 +229,15 @@ def test_boundary_mask(datastore_name):
     assert isinstance(da_mask, xr.DataArray)
     assert set(da_mask.dims) == {"grid_index"}
     assert da_mask.dtype == "int"
-    assert set(da_mask.values) == {0, 1}
-    assert da_mask.sum() > 0
-    assert da_mask.sum() < da_mask.size
+    assert set(da_mask.values).issubset({0, 1})
+
+    if "global" in datastore_name:
+        # global datastores have no lateral boundaries
+        assert da_mask.sum() == 0
+    else:
+        # LAM datastores must have a boundary
+        assert da_mask.sum() > 0
+        assert da_mask.sum() < da_mask.size
 
     if isinstance(datastore, BaseRegularGridDatastore):
         grid_shape = datastore.grid_shape_state
diff --git a/tests/test_training.py b/tests/test_training.py
index e8c131572..930742c41 100644
--- a/tests/test_training.py
+++ b/tests/test_training.py
@@ -41,10 +41,7 @@ def run_simple_training(datastore, set_output_std):
         max_epochs=1,
         deterministic=True,
         accelerator=device_name,
-        # XXX: `devices` has to be set to 2 otherwise
-        # neural_lam.models.ar_model.ARModel.aggregate_and_plot_metrics fails
-        # because it expects to aggregate over multiple devices
-        devices=2,
+        devices=1,
         log_every_n_steps=1,
         # use `detect_anomaly` to ensure that we don't have NaNs popping up
         # during training
@@ -124,3 +121,11 @@ def test_training(datastore_name):
 def test_training_output_std():
     datastore = init_datastore_example("mdp")  # Test only with mdp datastore
     run_simple_training(datastore, set_output_std=True)
+
+
+def test_training_global():
+    """
+    Test training with a global datastore (no boundaries).
+    """
+    datastore = init_datastore_example("dummydata_global")
+    run_simple_training(datastore, set_output_std=False)