Content Analysis will cache malicious results of scanning to reduce the time required to provide a result for matching files which have been previously scanned. There are options to clear the cache manually. However, this cache will clear periodically.
Content Analysis did not contain a sandbox clean cache option until CA 2.x
Content Analysis cache has TTLs for File Reputation Service, Predictive Analysis, and Sandboxing.
The AntiVirus cache will clear under the following situations
The AntiVirus cache is never persisted to disk (so it does not survive a reboot, for example) and changes in the conditions described. (McAfee, Kaspersky, or Sophos, Symantec)
Manual clearing of the cache can be performed from the UI of the Content Analysis within the Utilities menu under the Cache option. Here you will find four options of clearing cache for Antivirus, File Reputation, Sandboxing, and Static Analysis as separate buttons. After update to CA 2.x, there is a "clear all caches" button, as well.