This design is really similar to the approach taken by litefs[1] and turso[2]. Writes are forwarded to the primary (like you would with a write-through cache) and a local copy of the data is held in each region. These local copies are only guaranteed to be up-to-date with the most recent write forwarded by that local copy.

[1] https://fly.io/docs/litefs/proxy/ [2] https://docs.turso.tech/reference/data-consistency#on-the-re...