Starting with version 1.4 AD cmdlets can retrieve and provide detailed information on all properties for foreign security principals.
When you add a user from a trusted domain to a group in your domain, AD creates a local auxilliary object – foreign security principal – to represent this external account. You can essentially think about this object as a pointer to the actual account in a trusted domain. You can read more about them in the Security Principals section of this TechNet article.
Now QAD cmdlets can resolve these “pointers” and show you real accounts to which they point.
For example, this command will retrieve all foreign security principals which you have in your domain (i.e. all foreign accounts ever granted any rights) and try to resolve them to external accounts from original domains:
Get-QADObject -ResolveForeignSecurityPrincipals -Type foreignSecurityPrincipal