Unfortunately it seems to not be so easy:
rtadmin@ubt18-test:~$ cat /etc/nsswitch.conf
...
#passwd: compat systemd sss
#group: compat systemd sss
passwd: files sss
group: files sss
shadow: files sss
gshadow: files
...
rtadmin@ubt18-test:~$ getent passwd user1
user1:*:30335:33111:User One:/users/user1:/bin/bash
rtadmin@ubt18-test:~$ groups user1
user1 : unix_users groups: cannot find name for group ID 33118
33118
Curiously, when I did `getent passwd user1` it seems to have resolved and cached the primary group, but not any secondary groups.
Discussing `sss_cache -E`,
rtadmin@ubt18-test:~$ sudo sss_cache -E
rtadmin@ubt18-test:~$ groups user1
user1 : groups: cannot find name for group ID 33111
33111 groups: cannot find name for group ID 33118
33118
rtadmin@ubt18-test:~$ groups user2
user2 : groups: cannot find name for group ID 33111
33111
rtadmin@ubt18-test:~$ getent passwd user2
user2:*:30255:33111:User Two:/users/user2:/bin/bash
rtadmin@ubt18-test:~$ groups user2
user2 : groups: cannot find name for group ID 33111
33111