Page metadata isn’t the sort of thing that should change very often, but you can manually clear the cache by going to Facebook’s Debug Tool and entering the URL you want to scrape
There’s also an API for doing this, which works for any OG object:
curl -X POST \
-F "id={object-url OR object-id}" \
-F "scrape=true" \
-F "access_token={your access token}" \
"https://graph.facebook.com"
An access_token is now required. This can be an app or page access_token; no user authentication is required.