Just to clarify, you need something like the iMacros CLEAR command?
(imacros) CLEAR:
Clears the browsers cache and all cookies. Can be useful, for example, to delete Web site cookies so every macro run starts at the same point. It is also useful to use this command before doing website response measurements.
The Ui.Vision equivalent would be the deleteAllCookies command.
For something more powerful, see How to programmatically clean cookies and the browser cache and autocomplete and the browsing history.
Yet another cache clearing option is to tell Chrome to clear everything on exit.