Of course just because it's clumsy, buggy, error prone, and just plain stupid, doesn't mean it's impossible:

use strict;
use warnings;


our $var  = 10;
our $keep = 20;


print "\$var  = $var\n";
print "\$keep = $keep\n";

print "Reset <<\$$_>>\n" for dangerous_reset(qr/^v/);

print "\$var  = $var\n";
print "\$keep = $keep\n";


sub dangerous_reset {
  my $criteria = shift;
  my $package = (caller)[0] . '::';
  {
    no strict 'refs';
    my @wanted = grep {    /$criteria/                      # Meets cr
+iteria
                        && defined *{$package . $_}{SCALAR} # Has scal
+ar element
                        && /^[\p{alpha}_]\w*$/              # Isn't sp
+ecial.
                 } keys %{$package};
    undef ${*{$package . $_}{SCALAR}} for @wanted;
    return @wanted; # Return count, or list of variables removed.
  }
}
[download]

We had a troll here a few years ago who kept pushing some strategy he had for resetting variables programatically. I'm sure his kludge was a lot better thought out than the code I've shown here, but it was still a terrible, bug-prone, broken sledge-hammer of a tool. It's just not how things should be done.