我正在调试一个HTTP 301永久重定向的问题。经过快速测试，Safari似乎在重新启动时清除了它的301缓存，但Firefox却没有。

IE、Chrome、Firefox和Safari什么时候清空它们的301缓存?

For example, if I want to redirect 1.example to 2.example, but I accidentally set it to redirect to 3.example, that is a problem. I can correct the mistake, but anyone who has visited 1.example in the meantime will have cached the incorrect redirect to 3.example, and so they will not be able to reach either 1.example or 2.example until their cache is cleared. Upon investigation, I find that there were no Cache-Control and Expires headers set. The headers for the incorrect 301 response would have been like this:

HTTP/1.1 301 Moved Permanently
Date: Wed, 27 Feb 2013 12:05:53 GMT
Server: Apache/2.2.21 (Unix) DAV/2 PHP/5.3.8
X-Powered-By: PHP/5.3.8
Location: http://3.example/
Content-Type: text/html

我自己的测试表明:

IE7, IE8, Android 2.3.4完全不缓存。 Firefox 18.0.2、Safari 5.1.7(适用于Windows 7)和Opera 12.14都有缓存，并在重新启动浏览器时清除缓存。 IE10和Chrome 25缓存，但不清楚浏览器重启，所以他们什么时候会清除?