this is an interesting question! As far as I understand Zanzibar was designed for global replication but I'm not 100% sure it mentions anything about data domiciling. This is not supported out of the box by SpiceDB. I think it would be possible but the main challenge would be how to expose it via the API when not all datastores support this concept. It would require a bit of a refactor of the datastore implementation to make sure:
- datastore is aware of data domiciling
- relationships have a column with such information
- as authorization decisions are computed, the datastore collects only those relationships that are either global or specific to the region the request is originating from.
It would be a bit of an undertaking but I think it's an interesting topic and one that could be implemented. Would you mind filling an issue with your requirements?