On D7, exec via drush returns "The drush command 'delete_all' could not be found."

I just installed/enabled 'delete_all' on D7.14

drush @TEST pm-info delete_all
 Extension        :  delete_all
 Project          :  delete_all
 Type             :  module
 Title            :  Delete content and users
 Description      :  Allows deletion of all nodes, comments and users on a site. Useful for development or prior to
                     launching a site.
 Version          :  7.x-1.x-dev
 Package          :  Development
 Core             :  7.x
 PHP              :  5.2.4
 Status           :  enabled
 Path             :  sites/all/modules/contrib/delete_all
 Schema version   :  module has no schema
 Files            :
 Requires         :  none
 Required by      :  none

Trying to delete existing content via drush, it fails with "The drush command 'delete_all' could not be found"

drush --version
	drush version 6.0-dev

drush @TEST delete_all
	The drush command 'delete_all' could not be found.  Run `drush cache-clear drush` to clear the commandfile[error]
	cache if you have installed new extensions.

drush @TEST cache-clear drush
	'drush' cache was cleared                                                                                 [success]

drush @TEST delete_all
	The drush command 'delete_all' could not be found.  Run `drush cache-clear drush` to clear the commandfile[error]
	cache if you have installed new extensions.