Kill all applications in switcher
1. First kill all the applications
[(SBSyncController *)[NSClassFromString(@"SBSyncController") sharedInstance] _killApplications];
2. then remove the applications from the switcher
iOS 8
[[[NSClassFromString(@"SBAppSwitcherModel") sharedInstance] valueForKey:@"_recentDisplayLayouts"] removeAllObjects];
iOS 7
[[[NSClassFromString(@"SBAppSwitcherModel") sharedInstance] valueForKey:@"_recentDisplayIdentifiers"] removeAllObjects];