ASIHTTPRequest Clearing Cache for only one URL
===

I'm using ASIHTTPRequest with caching for downloading pictures in my iOS app.  Most pictures never change and hence can leverage the caching functionality.  There are a few that do change based on a certain function in the iOS app.  So, I know exactly when these images will change.  How can I clear the cache of a certain link (e.g. http://www.test.com/image.jpg) and preserve the cache for all other requests in my app.  Thanks. 

    ASIHTTPRequest *request;
    request = [ASIHTTPRequest requestWithURL:[NSURL URLWithString:@"{Image url}"]];
    [request setDownloadCache:[ASIDownloadCache sharedCache]];
    [request setCachePolicy:ASIAskServerIfModifiedWhenStaleCachePolicy|ASIFallbackToCacheIfLoadFailsCachePolicy];
    [request setCacheStoragePolicy:ASICachePermanentlyCacheStoragePolicy];
    [request setSecondsToCache:60*60*24*7];