A good place to start
is right here.
You might need to set up a few notifications depending on how many types of cache you are interested in being notified about. Follow the instructions on the page above. As soon as you have chosen the type to watch, for example 'Traditional Cache' you will be presented with options to what you can be notified about. Follow the rest of the instructions as on the page above.
Hopefully you will be able to work out from there, but if you need any more help then just ask