I have kept separate flocks and let them free range during the day. In my experience, the different flocks kind of went their own way. Not a lot of fighting, really, but we have enough space for them to be away from each other, too. Generally, if a flock is accustomed to sleeping in a certain coop, they will return to that coop on their own at night. When they get it in their heads where "home" is, it sticks pretty well.