Emails not going to a specific domain that we were hosting

Hi,
I'm running into an issue and i know it's something easy that I'm missing.  Maybe one of you experts can help me out.  I used to house two email domains on my exchange server.  A.com and B.com.  Company B is small and in another location so we thought it would make more sense to set them up on google apps for business.  I went ahead and set them up on it.....got all the MX records into the domain settings.  All emails flow to them except from inside company A (my exchange server).  I know i'm missing something somewhere.  I notice if a create a new user with an exchange mailbox it will create to email addresses xxxx@A.com (default) and xxxx@B.com (secondary).  So i know something is set up somewhere for company B that I for some reason can not find.  Any help?