How to get google cache date

[reygcalantaol]

I am developing google search application using google search API.
I am almost done with it but I have one problem which I am hardly find the solution over the net.

My problem is to get the cache date (a date where google last crawled the site).

I will be making a function that accepts URL:

function getCacheDate($url) {

//PHP Code to retrieve cache date

return cachedate;
}

If anyone can supply even javascript code is appreciated.