IP Schema

Forgive me for sounding a little unknowledgeable but I have a multi-site org of which I am supporting and bringing up DC's at every site. The routing aspect in terms of configuration is done but the one thing that worries me is the DC's communicating even though they are in different subnets. Site A has a 192.168.1.x sub, Site B will have a 192.168.2.x sub and Site C will have a 192.168.3.x sub and so on and so forth. DC for Site B is currently sitting next to the DC that supports Site A for replication purposes so they are both sitting in the same subnet until I make the move to Site B. Do I have to add the subnet/primary zone to the DC of which will b supporting site 2? Please advise.