It is possible to keep users connected only to the Videobridges belonging to theirs region?

Let us suppose that we have two regions configured with Octo: RegionA and RegionB .
Each Region has two Videobridges:
RegionA : VB_A1 and VB_A2
RegionB: VB_B1 and VB_B2

Normally each user get connected to a Videobridge belonging to his region.
I’m under the impression that if we shut down all the Videobridges for RegionA,
then all the users will be sent to the remaining Videobridges ( RegionB).

Is this the case?
My point is: how can this be avoided ?
How can we keep each user strictly connected only to his Regional Videobridges ?

Thank you for your time and for your great work !