You can attach a cache dependency to the response that is unique per query param, then invalidate the dependency for that particular param:
// add cache item dependency on response
string cacheKey = 'xxx.aspx?' + queryParam;
Cache[cacheKey] = new object();
Response.AddCacheItemDependency(cacheKey);
// invalidate the dependency
string cacheKey = 'xxx.aspx?' + queryParam;
Cache.Remove(cacheKey);
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