@listToExpire = grep { $b = (@{$_})[0] &&
 grep { $a = (@{$_})[0] && $b != $a } @listA
 } @listB;

##</code><code>##

@listToExpire = grep { $b = (@{$_})[0]; grep { $a = (@{$_})[0]; $b != $a } @listA } @listB;