In legacy stack. In legacy root dir.
When executing the command line :

php bin/php/ezcache.php --clear-id=imagealias --purge

then the variations image aliases are not removed from the corresponding XML stored in ezcontentobject_attribute.data_text. This is the "ezimage" datatype. The XML has the following format :

<ezimage>
    <original attribute_id="256" .../>
    <alias name="reference" .../> <!-- not removed -->
    <alias name="small" .../> <!-- not removed -->
</ezimage>

The issue is located in eZImageAliasHandler::purgeAllAliases(), the DomNode::removeChild() call has not the expected result when a loop is done from a DOMNodeList object.
See the DomNode::removeChild() documentation :
http://php.net/manual/fr/domnode.removechild.php#90292