FBSession* session = [FBSession activeSession];
[session closeAndClearTokenInformation];
[session close];
[FBSession setActiveSession:nil];

NSHTTPCookieStorage* cookies = [NSHTTPCookieStorage sharedHTTPCookieStorage];
NSArray* facebookCookies = [cookies cookiesForURL:[NSURL         URLWithString:@"https://facebook.com/"]];

for (NSHTTPCookie* cookie in facebookCookies) {
    [cookies deleteCookie:cookie];
}