copy root files to child domains from the root Forest?

[blade10]

Hello-

I have one forest but many child domains across the world with site bridge links.

I have heard that engineers have "copied" certain root files to these long distance child domains in order for replication and other things to work correctly with the schema under the one forest location.

what exact files are they talking about? is it certain metadata files, ntds.dit? if so, where are they placing these files on the child domain?
if there is a url for additional reading I would truly appreciate the information

blade