Identity server single sign out, logout from server too

Identity server single sign out, logout from server too

Here is my logout code that I use in relying party:
FederationConfiguration cfg =
FederatedAuthentication.FederationConfiguration;
var fam = FederatedAuthentication.WSFederationAuthenticationModule;
fam.SignOut(false);
var signOutRequestMessage = new SignOutRequestMessage(new
Uri(fam.Issuer), fam.Realm);
return new RedirectResult(signOutRequestMessage.WriteQueryString());
And get logout from RP and redirected to Identity server "Signed out"
page, but I still remain logged in at Identity server, is this expected
behaviour? How can I change this so I get logged out from Identity server
also?