You can use the 'state' feature' (refer: perldoc perlfunc) rather than the extra block to limit the scope of $last.

use feature 'state';
 
   sub do_stuff {
       
       state $last=999;
       my ($arg) = @_;
         if ( $arg == $last ) {
             print "You called me twice in a row with $arg\n";
         }
     $last = $arg;
    }

do_stuff($_) for 0..5,5;
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