How do you prevent double spend in the intervening period?
the risk is that a transaction you've accepted gets invalidated by a competing spend of its inputs in a chain coming out of a different "network zone"
so you wait for more block confirmations
So it would be very difficult to prevent transactions from leaking out of or into the isolated zone:
A single peer in the whole country which is connected to the outside would be enough to leak all transactions.
[1] https://en.wikipedia.org/wiki/Flooding_(computer_networking)