Closing USD Stage

[cadop]

In the notebook there is an example for opening a USD stage: ColaboratoryNotebooks/opening_stages.ipynb

It would be nice to show at the end of it, how to close the stage. I may just have an unrelated problem that is manifesting this way, but in the worst case, maybe a comment at the end of the tutorial on what "open" vs. "close" would mean.

Use case:
I have a sort of circular reference problem, where I open a stage X, I open a new stage Y, but Y is referenced in X. I got what I needed out of X (e.g. points of a mesh), so I don't need it anymore.

    self.stage = stage = Usd.Stage.CreateNew(stage)
pxr.Tf.ErrorException:
        Error in 'pxrInternal_v0_23__pxrReserved__::SdfLayer::_CreateNew' at line 616 in file D:\a\1\s\pxr\usd\sdf\layer.cpp : 'A layer already exists with identifier 'XXX/Y.usd''

Maybe its not using nucleus/usd correctly, but the point is that I want to have a scene with a reference to another scene inside it. I do some operation on the referenced scene, and want it to update (fetch) to see the results.