You could now try another scan and see if anything is picked up.
Whilst I don't use a Mac, I think this would apply there also.
With a resident (on-access) scanner the need for on-demand scans is much depreciated. For the most part dormant/inert files are being scanned, the other active files are going to be scanned by the resident shields when they are activated.
In your case it would only be if that browser cached item were still present and initiated, then if this redirect occurred, it should cause the Web Shield to alert.
Personally I rarely ever use the on-demand scans, usually this is as a result an enquiry in the forums.