I have two internet service providers, comcast and at&t

I have one computer on each...

I want to set up each computer's update client to update the appropriate domain/sub domain
but it doesnt seem to do that..

for example:
I have a domain and a subdomain. x.com and y.x.com
On the computer on comcast, i run the update client and i want it associated with x.com
On the at&t compute i run the update client and i want it associated with y.x.com

Thats not what happens....whichever computer i run it on, it updates both to that computer
The client doesnt seem to allow me to say what domain i want it to run on.

Any assistance would be appreciated