google plus iOS app logout issue

i have made an iOS app in Xcode and did a google plus integration for login in it using http://ift.tt/IImK38 The login part runs perfectly ok. but the issue is with logout. actually the problem is after login when i press logout button it does not actually log me out. after logout when i login again instead of asking me username and password it actually stick on the previous user login account i.e logout does not clear the login session after logout.the sign out and disconnect methods does not create any impact .so please suggest me a way to logout.

thank u in advance.