If you want to stop the server side processing then its a tricky operation. Generally once a request is made that page is rendering on its own independant of other thigns going on. What you would probably need to do is re-engineer that page to check at regular intervals whether a stop command has been issued and abort whatever it is doing at that point. The stop flag could be put in session and should be cleared out after the stoppage.
You may also need to consider how to properly identify the right one to stop (in case there is more than one running). This could be done by returning a unique ID that can be used in part of a call to the "abort" page.
My approach though rather than this complciated rigmarole is to make efforts to stop the user from making this accident. Possibly make whatever link they are clicking pop up an alert saying "the following page will take several minutes to render, do you wish to continue" and then hopefully you will effectively be aborting the page request before it is even made.
I should note that I've never tried to do this sort of thing before so there may be easier ways to do it but this is how I'd probably think abotu going about the problem.