for my $k ( keys %harry ) {
   my $a1 = $harry{$k};
   my $a2 = $harry{$phash{$k}};

   my %seen;
   ++$seen{$_} for @$a1, @$a2;

   @$a1 = grep $seen{$_}>1, @$a1;
   @$a2 = grep $seen{$_}>1, @$a2;
}