Guest traffic goes through anchor wlc

[interfacedy]

Hi, We have three sites offices(A, B, and C). On each site, there are one pair of WLC(c9800) and several APs. Now we want all guest traffic go through one pair of anchors like below diagram. My question is which device is Foreign WLC? Is this topology is correct? Thank you 

[Arshad Safrulla]

In Anchor controllers prospective all WLC's at site A,B & C are foreign controllers.