You can check via the Graph API using the ids query.
https://graph.facebook.com/?ids=http://apple.com
{
"http://apple.com": {
"id": "http://apple.com",
"shares": 141119
}
}
Depending on the website and whether a Like button was available on that page you may get the number of shares instead.
https://graph.facebook.com/?ids=http://www.imdb.com/title/tt1375666/
{
"http://www.imdb.com/title/tt1375666/": {
"id": "110935752279118",
"name": "Inception (2010)",
"picture": "http://profile.ak.fbcdn.net/hprofile-ak-snc4/71156_110935752279118_1973266_s.jpg",
"link": "http://www.imdb.com/title/tt1375666/",
"category": "Movie",
"website": "http://www.imdb.com/title/tt1375666/",
"description": "Directed by Christopher Nolan. With Leonardo DiCaprio, Joseph Gordon-Levitt, Ellen Page, Ken Watanabe.",
"likes": 46015
}
}