I own this aliens/UFO site and today I noticed the cache of the site in Google is not what my site actually looks like and I'm wondering why and how this happen. http://74.125.113.132/search?q=cache:k1jWenDtWjgJ:www.alien-ufos.com/+alien-ufos.com&cd=1&hl=en&ct=clnk&gl=us
Your cache will get updated once a Google Bot visits the page again. The more quality links pointing to your domain and or web page the faster Google will update the cache. Also if the page doesn't change don't expect the cache to be updated as nothing has changed within the webpage.