Sticky cache, when Memcached is not used

When we are not using any particular caching engine (e.g. memcache, apc),
then default caching handler is used.

Such default handler will only cache values until script execution is
finished. This can became a problem, since no automatic cache key reset
system is used in such case.

For example, when you cache product price and then change that price in
database, then you still will get same old price from cache.