Question

I like the share button more than the like button, thats why i’m using it. The problem is that if the title of the page change and when someone paste it into facebook is still with the old title

Sample code

I put span with a tag in the bottom of the page

http://www.facebook.com/share.php?u=http://stackoverflow.com

Answer 1

Using the share functionality is not a good decision since it has been deprecated and is no longer supported, as it clearly states here:

The Share button has been deprecated in favor of the Like button, and
will no longer be supported. Please use the Like button whenever
possible to drive maximum traffic to your apps.

And here:

What happened to the old Share button?

We deprecated the Share Button when we launched the Like button,
because the Like button improves clickthrough rates by allowing users
to connect with one click, and by allowing them to see which of their
friends have already connected.

With that said, to answer your question, it also written in the Like Button guide:

When does Facebook scrape my page?

Facebook needs to scrape your page to know how to display it around
the site.

Facebook scrapes your page every 24 hours to ensure the properties are
up to date. The page is also scraped when an admin for the Open Graph
page clicks the Like button and when the URL is entered into the
Facebook URL Linter. Facebook observes cache headers on your URLs – it
will look at “Expires” and “Cache-Control” in order of preference.
However, even if you specify a longer time, Facebook will scrape your
page every 24 hours.

The user agent of the scraper is: “facebookexternalhit/1.1
(+http://www.facebook.com/externalhit_uatext.php)”

To clear the cache the easiest thing is to just use the Debug Tool.