Question: Ajax cache pages history

I am now learning how to use jquery to cache ajax requests. I would like to know the answers to the following questions:
How can I go back to a cached ajax request? Lets say I made an ajax request which brought up new content and I want to go back to the previous ajax request (which was done initially) by pressing the back button how can this be done?
In using ajax cacheing how can I ensure that when new content is added that the cache pages are replaced?

You can update the hash tag every time you are at a state that you want to be able to go back to.
How it would work is when the page is loaded with a hash tag, the page request the information that it needs, using the hash tag as a guide for what info to get.

excellent do you have any good tutorials on how to do this with jquery ajax. Note that some states I may want to change need parameters so if the tutorial covers that also that would be great.

thanks alot will take a look at this now.