Hi Doug,
If you have logically the same attribute in multiple datasets (as several separate attributes), and want to filter them with one filter, you can create a new dataset, move one of these attributes there and mark it as a primary key. Then replace the other attributes by a reference to this newly created dataset. I would recommend checking this article:
https://university.gooddata.com/tutorials/data-modeling/logical-data-model-basic-rules-of-data-modelling/ specifically the point 3.
Just make sure you do not introduce an alternate path between other datasets by this change as described in point 5. of that article.
And also be careful when replacing those attributes if you are already using them (in that case maybe first add the reference, update your metrics/visualizations and only then remove the original attributes).