Under US Part 121, it is all done form a central office. For instance, I will release both CGN-EWR and EWR-CGN flights on a shift. I hesitate to say All, but I believer all US carriers operate from one dispatch office.
Now, as a non US carrier, I don't know. Some carriers have(or had at one time) a US dispatch office (Lufthansa comes to mind, but that was a while back).