I'm sorry, but Charles Goodwin is right. The "approach" itself doesn't take a preposition at all.
I'm approaching you.
Obviously, if I'm approaching you for a reason or to get some results has nothing to do with the approaching itself.
I might just as well use another verb and the situation would be the same:
I'm approaching you for a reason.
I'm flattering you for a reason.
I'm approaching you to get some results.
I'm flattering you to get some results.
Please observe how for introduces a noun (a reason) and to introduces a verb (to get). That's why in some cases you should use for and in others you should use to.
Now the catch with the caching is that it can be both a noun (the caching) and a verb (to cache as the gerundive mood). So obviously both forms are correct!
Happy caching, don't forget to invalidate often and have fresh data for your users :)