Title: #153: sss_cache: User/groups invalidation in domain cache
This approach seems less intrusive than the previous one and the integration tests passed
locally (already asked @celestian to run our CI as well).
I'll do a proper review of the patches later Today/Tomorrow and I'm removing the
"Changes requested" label for now.
See the full comment at https://github.com/SSSD/sssd/pull/153#issuecomment-279684152