Today Microsoft released CU3 version of ConfigMgr 2013 R2, and there are some minor bugfixes but there is also one important new change here!
That is the ability to define allowed Management Points for a client to communicate with,
This cumulative update introduces a new registry key on clients that will restrict which management point (MP) a client can communicate with. This can be useful in environments with multiple MP’s in different forests, and the clients are only able to communicate with a subset of them. Setting the registry value to only those MP’s reachable by the client can improve overall efficiency. The new registry value is AllowedMPs, a REG_MULTI_SZ (multi-string) type under HKEY_LOCAL_MACHINE\Software\Microsoft\CCM
Each entry is the Fully Qualified Domain Name of the management point(s) with which the client is allowed to communicate. This value does not affect the selection of any other site systems such as distribution points, software update points, etc.; it only affects the primary site MP selection. Note: Once defined, there is no “fallback” or other method for clients to communicate with other MP’s. It is not intended for mobile clients.”
From the KB http://support.microsoft.com/kb/2994331