which level in Active Directory would you deactivate UGMC?

You need to deactivate the UGMC option on some of your domain controllers.
At which level in Active Directory would you deactivate UGMC?

A.
Server

B.
Site

C.
Domain

D.
Forest

Explanation:
http://www.ntweekly.com/?p=788
Question:How To Enable
Or Disable Universal Group Membership Caching Windows Server 2008
Group Membership Caching enables us to allow users to log on to the network without
contacting a Global Catalog server, this is recommended to use in remote sites without
global a catalog server.
To enable or disable Universal Group Membership Caching follow the steps below:
Open Active Directory Sites And Service -> Go to the site you need to enable or disable the
feature -> Right click on the NTDS Site Settings and Click on Properties

Tick the Box next to Enable Universal Group Membership Caching to Enable or Disable.

http://gallery.technet.microsoft.com/scriptcenter/c1bd08d2-1440-40f8-95be-ad2050674d91
Script to Disable Universal Group Membership Caching in all Sites
How to Disable Universal Group Membership Caching in all Sites using a Script
Starting with Windows Server 2003, a new feature called Universal Group Membership
Caching (UGMC) caches a user’s membership in Universal Groups on domain controllers
authenticating the user. This feature allows a domain controller to have knowledge of
Universal Groups a user is member of rather than contacting a Global Catalog.
Unlike Global group memberships, which are stored in each domain, Universal Group
memberships are only stored in a Global Catalog. For example, when a user who belongs to
a Universal Group logs on to a domain that is set to the Windows 2000 native domain
functional level or higher, the Global Catalog provides Universal Group membership
information for the user’s account at the time the user logs on to the domain to the
authenticating domain controller.
UGMC is generally a good idea for multiple domain forests when:
1. Universal Group membership does not change frequently.
2. Low WAN bandwidth between Domain Controllers in different sites.
It is also recommended to disable UGMC if all Domain Controllers in a forest are Global
Catalogs.