Case: The website has mostly anonymous visitors and a few content changes every so often. Waiting on cron to run may not be the best solution if you want changes to be available for anonymous visitors immediately. On a website such as this you are taking advantage of the Boost timestamp function to rebuild only pages that have changed at each cron run. This rules setup works outside of that Boost function as it will immediately refresh the cache with the one page that has has changed.

Solution: Download the rules module, unzip it and upload it to sites/all/modules. Goto: (Administer > Site building > Modules > List) to enable Rules, save the changes. Goto: (Administer > Rules > Triggered rules > Add a new rule). Give the new rule a label or name, choose an Event that will trigger the rule from the select list (Content is going to be saved), check mark the box [X] This rule is active and should be evaluated when the associated event occurs. and save the changes. In the next section, choose (Add an action). Use the select list and choose (Clear a page from the boost cache), Next, then Save.