There are a lot more things that you'll need to worry about than just raw <script> tags.

For example:

<a href="http://example.com" onClick="alert(1);">test</a>

To deal with this complexity properly you should be looking at using one of the filtering modules available from CPAN.

I've got good experience of using HTML::Scrubber - but there are a few more including HTML::EscapeEvil and HTML::Sanitizer