[Samba] domain memership and security=domain

[Julian Pace Ross]

I apologise for re-posting, but I'll try summarise just in case my original 
message was confusing...

I have successfully deployed my first Samba 3 PDC with LDAP.

I have another Linux PC (separate from the PDC) that is  acting as a file 
server, with it's own shares.

This PC has no local user accounts, and I set this with security = domain, 
passwd server = SambaPDC.
It successfully joined it to the domain with net  rpc join etc..

On each share I specify which users can access that share (valid users = )

Should security = domain mean that only  workstations already joined to the 
domain can have access to the file server shares?
Until now, I can still access the shares even from the non-domain 
workstations.
In other words, can a Samba3 domain member limit access to its shares only 
to other PCs that are also domain members?
Or, even better, can this be specified specifically per share?

Thanks and regards
Julian