processAorB ....{
   my @commonArray;
   commonStuff( \@commonArray, \%other, \$variables );
   ...
}
sub commonStuff {
   my ( $commonArrayRef, $hash, $var ) = @_;
   if ( $commonArrayRef->[0] > 37 ) { ...
 
   }
}

##</code><code>##

sub processA {
   ...
   commonInit()
   commonStuff( $various, $vars );
}
sub processB {
   ...
   commonInit()
   commonStuff( $various, $other, $vars );

}
{
    my @commonArray;

    sub commonInit {
        @commonArray = ();
    }

    sub commonStuff {
        # do stuff to @commonArray;
    }
}