One of the largely unheralded big new features of Active Directory Certificate Services is that it can now be configured to be site-aware!
This is accomplished by following the detailed steps that are described on the ADCS Wiki link below.
The short version is however as follows:
...then add some suger and bake for 30 minutes in the oven, that's it! :)
AD DS Site Awareness for AD CS and PKI Clientshttp://social.technet.microsoft.com/wiki/contents/articles/14106.ad-ds-site-awareness-for-ad-cs-and-pki-clients.aspx
What's New in AD CS [in Windows Server 2012]?http://technet.microsoft.com/en-us/library/hh831373.aspx
FYI the registry change is *not* required on Windows 8 as the functionality is included by default. The wiki entry here: social.technet.microsoft.com/.../14106.ad-ds-site-awareness-for-ad-cs-and-pki-clients.aspx has recently been updated to reflect this.