Cisco Cisco Web Security Appliance S660 Mode D'Emploi

The following guidelines explains how AsyncOS uses the cache while scanning for malware: 

AsyncOS only caches objects if the entire object downloads. If malware is blocked during scanning, 
the whole object is not downloaded and therefore is not cached.

AsyncOS scans content whether it is retrieved from the server or from the web cache.

The length of time that content is cached varies with many factors - there is no default. 

AsyncOS rescans content when signatures are updated.