Active Directory with Multiple Domains and LDAP Auth

Hello All,
I have an Active Directory forest with 3 domains
abc.com, abc.exch and abc.users
All are sibling domains. I have an application that runs on one Domain COntroller that is abc.com and performs a LDAP Search on LOCALHOST on port 389 but when it does that it can see only objects belonging to abc.com. Is there anyway where if i do a LDAP search on LOCALHOST on 389, it should search the entire forest rather than only that domain?
 
Please advise!!
 
Regards