To do a mass purge, one can update the value of
$wgCacheEpoch (this
would also be accomplished by touching LocalSettings.php where that
file was generated by a more recent installer, but I suspect your wiki
was established long before that was the case) in LocalSettings.php.
The 1.7.1 LocalSettings.php has
# When you make changes to this configuration file, this will make
# sure that cached pages are cleared.
$configdate = gmdate( 'YmdHis', @filemtime( __FILE__ ) );
$wgCacheEpoch = max( $wgCacheEpoch, $configdate );
so touching it should have been enough it seems.