windows domain scan issue

we have two office, on office location is hk. and the others is mainland PRC.and now, we have a problem with SD plus windows domain scan issue.
1.the hk office SD plus can scan the local pc (only hk's pc)but can't scan mainland pc.
2.installed a doem SD plus in mainload office, and now, can't scan hk office pc.all mainland pc can scaned.
3.two domain, the hk domain is abc.domain, the mainland domain is efg.domain.
4.client pc inclued xp+sp2(enable firewall) and windows 2000, I can't ping a hk office slamp pc name form mainland office(eg. ping computername) ,but can ping fullname(eg. ping computername.abc.domain)
how to fix the issue??

thanks!