The --purge parameter of bin/php/ezcache.php overrides the --expiry parameter, and clears everything. This is undocumented, and undesirable IMHO. The attached patch solves this.

Steps to reproduce

bin/php/ezcache.php --clear-id=template-block --expiry='-2 days' --purge

In this case, all template blocks will be deleted. I would expect that only the template blocks older than two days (48 hours) would be deleted.