If the clients roam between APs registered to different controllers and the client WLAN on the two controllers is on different subnet, then it is called inter-controller L3 roam.
In this situation as well controllers exchange mobility messages. Client database entry change is completely different that toL2 roam(instead of move, it will copy). In this situation the original controller marks the client entry as "Anchor" where as new controller marks the client entry as "Foreign". The two controllers now referred to as "Anchor controller" & "Foreign Controller" respectively. Client will keep the original IP address & that is the real advantage.
Note: Inter-Controller (normally layer 2) roaming occurs when a client roam between two APs registered to two different controllers, where each controller has an interface in the client subnet.