when trying to connect to a Samba member server with an invalid domain name and a valid *local* user name Samba returns NT_STATUS_NO_LOGON_SERVERS when no DC is available even though it should authenticate against its local SAM. Only if the correct server's name is given, the authentication is working in that situation:
# smbclient //localhost/test -UFOOFAA\\testx%xxx
session setup failed: NT_STATUS_NO_LOGON_SERVERS
Doing the same test against a Windows member server results in successful authentication against the local SAM. The Windows server caches the known trusted domains also and (only) lets the authentication fail if the auth attempt is done with a user of a trusted domain (or the joined domain of course). Samba should behave the same way.