Jodie,
By itself the ASA doesn't cache any content (there is no storage capacity on the device itself to have decent cache size).
That being said, things I would look into:
- is http inspection enabled? (show run policy-map)
- url filtering used?
- is CSC or IPS module installed? (show modu) and is the webpage traffic going through it?
- Maybe WCCP configuration and ASA sending traffic somwehere?
Marcin