my $scrollbar = $mw->Scrollbar(-orient => 'vertical);
my $raListboxes = [ $mw->Listbox(), $mw->Listbox() ];

##</code><code>##

sub scrollListboxes
{
    my ($scrollbar, $scrolled, $raListboxes, @args) = @_;
    $scrollbar->set(@args);
    my ($top, $bottom) = $scrolled->yview();
    foreach my $listbox ( @$raListboxes )
    {
        $listbox->yviewMoveto($top);
    }
}

##</code><code>##

foreach my $listbox ( @$raListboxes )
{
    $listbox->configure(
       -yscrollcomand =>
       [
          \&scrollListboxes,
          $scrollbar,
          $listbox,
          $raListboxes
       ]);
}

$scrollbar->configure(
   -command => sub
   {
       foreach my $listbox ( @$raListboxes )
       {
           $listbox->yview(@_);
       }
   });