How do I restrict chrome greasemonkey scripts to a single webpage, or just certain webpages?

Use @match, as described here.

Example:

// ==UserScript==
// @match http://*/*
// @match http://*.google.com/*
// @match http://www.google.com/*
// @match https://www.google.com/*
// ==/UserScript==

using @include @exclude tags in metadata? http://diveintogreasemonkey.org/helloworld/metadata.html https://wiki.greasespot.net/Metadata_Block