What SOCAN is attempting, essentially, is an indirect patent on cache technologies. Web caches simply cache the most recently accessed (and/or most frequently accessed) web pages and URLs. They have absolutely no way of knowing what they are saving and whether or not it is violating a copyright.
The truth of the matter, however, is that probably over 99% of the web URLs held by cache systems are copyright clean. SOCAN is attempting to tax and/or impede access to that 99%+ for the <1% that ISPs are unable to filter out.
The cache mechanism isn't just used by ISP's Disk drives and CPUs also use them (most modern CPUs have at least two levels of cache attached to them).
Under normal conditions, there is no real way to access the contents of the cache other than pointing to the URL of the remote systems, and the average web user would have absolutely no idea that the data was coming from anywhere other than the targeted system. Technologically, the best way to change or remove an item from a cache is to change or remove the URL that is being cached.. Cache systems are designed to pick up such changes
and automatically update their local copy.
Cache systems are not intended to violate copyright, nor, for the most part, are they used in that way. Declaring cache technologies to be effectively illegal will simply increase the loads on the most popular (and generally copyright-clean) web sites.