Managing further domains in Universal Server

Hey guys,

I'm working for a bigger enterprise company with several sub-companies (sub-domains). So below of the global root domain I'm working for domain A which is designed as a shared service center in order to provide different services like Exchange, Enterprise Vault, Lync, etc. to the Domains A - Z
Now some domains asked for an encryption solution. Domain B got a ready configured PGP Universal server environment which is only used by domain B itself.

Is it possible to provide PGP from domain B to a different Active Directory Domain and what is necessary to do this?
What would be the requirements for this like domain trust and so on...

Thanks in advance.

Kind regards,
Chris