var ctxt, synchronizer;

ctxt = Packages.org.springframework.web.context.ContextLoader.getCurrentWebApplicationContext();
synchronizer = ctxt.getBean('userRegistrySynchronizer', Packages.org.alfresco.repo.security.sync.UserRegistrySynchronizer);

// forceUpdate = false, isFullSync = false - change for full update / with deletions
synchronizer.synchronize(false, false);