A trust is configured to allow users from domains other than the one QAS is joined with to access the system, however users in these other domains still do not show up on a vastool list until they have logged on.
By default, on a vastool flush only the users from the joined domain will be cached. You can add the user-search-path and group-search-path options to your vas.conf file to tell it to load users and groups from other domains:
user-search-path = OU=unix-users,DC=yourdomain,DC=com; OU=unix,DC=sub,DC=trusted,DC=com
group-search-path = OU=unix-groups,DC=yourdomain,DC=com; OU=unix,DC=sub,DC=trusted,DC=com
This can be set using vastool configure command or through Group Policy.