Is the following at all possible with extensions

Hi guys I have 3 Asterisk servers in different locations, and would like to know
if the following is at all possible.

I currently have it set up, so all extensions can call between different Asterisk servers.
I would like to set it so extensions can only talk with other extensions native to there Asterisk server, but only admins and myself can reach all Asterisk server extensions.
Do you guys think this could be done?
Thanks Sara~

use different context for admins

Thank you so much ambiorixg12 for the quick replay
your answer has been very helpful
Thanks for solving my problem