In Apache 2.2 there are 2 types of advanced caching available:
– Memory based caching
– Disk based caching
Here are some tips and links related to the disk cache feature:

APACHE 2.2 cache cleaning command:
Recomended to run regularly from cron job

# Runs as cron job, in nice mode, and limits the cache to 200MB
htcacheclean -n -t -p /var/www/cache -l 200M

Apache caching articles