For each Netscaler gateway VIP at that DC, i create two 'managed netscaler gateway' entries, one that uses the common URL (
citrix.domain.com), and one that uses a unique URL (
dc1citrix.domain.com) so i can directly target that DC. Those two entries would have the same callback URL.....the other DC would have their own entries with their own callback URL. That's how I did it.