I have a domain, eg dom.com, with various sub-domains, eg sub.dom.com. I would like to change the homepage of dom.com from index.html to index.php. To achieve this I added the line "redirect 301 /index.html http://dom.com/index.php" to .htaccess. Although this works for the main domain it also redirects the homepages of the subdomains to dom.com/index.php. How can I restrict the re-direct to the root directory of the top domain and leave sub-domains and sub-directories untouched?