How are cached usernames and passwords cleared from the memory of a R75 Security Gateway?

How are cached usernames and passwords cleared from the memory of a R75 Security Gateway?

A.
By using the Clear User Cache button in SmartDashboard

B.
By retrieving LDAP user information using the command fw fetchldap

C.
Usernames and passwords only clear from memory after they time out

D.
By installing a Security Policy