Dividing servers based on space is tricky, and causes issues with the "owner" of a space having disproportionate power, abuse of which is very hard to prove.
Instead, servers own entities (players, bots, etc), and the servers talk to each other in a distributed network and subscribe to events from each other
Within this network, things work pretty much like a traditional game, where everybody is a semi-trusted party for stuff like player positions
The challenge is now how to have the servers subscribe to each other properly.
For a small enough server count, simply doing pairwise connections can probably work well.