Resolution
This ins't really a cache issue per say, to get rid of the layout each person has customized, the UIPreferences object has to be deleted. This covers the dashboard layout, but it also covers things like certification column layout.
If this is what you want to 'reset', then they you either update each UIPreference with a templated object, or delete them via the Access Governance Suite Console, this can be done as a simple command in the console.
> delete UIPreference *
Deleting UIPreferences 2c90bc812e761d2f012e8070523f015f
Deleting UIPreferences 402881c62e23c637012e23dda2e208d8
Deleting UIPreferences 8a884bd42ca2e1ea012ca6a6ccd8003d
As with any Console command that Deletes anything please be sure to test this thourouly in your Test Environmet to make sure you get the desired results.
These are stored in different places in different product versions, so be very careful when doing this.
Additionally, there is much more than the items of interest to the customer stored in the UIPreferences object, so removing it would reset a lot of things and not likely be the path of least astonishment for your end users.