Enable/Disable Cache depending on the user login

A table needs to be maintained which maps the user name with the flag, determining that the cache should be purged on the user's logon or not.

After this, at each logon the Initialization block should run a query referring this table against that user, and sets dynamically a target repository variable.

Cache will be purged whenever the initialization block that populates dynamic repository variable is refreshed, which is at logon(set so).
P.S.: Its important to note here that the cache once purged would be affecting all users, which you would not want to hit performance, until the requirement is to purge the cache through a specific user's logon.