Preserving hash structure after subroutine call

Anonymous Monk has asked for the wisdom of the Perl Monks concerning the following question:

I have a hash structure that I'd like to keep intact after a subroutine call. I've tried several things, but nothing works. There's got to be something simple I've overlooked:

my %myhash;
build_hash(\%myhash);
print Dumper(\%myhash);  ## shows %myhash to be empty

sub build_hash {
   my $href = shift;
   my %results;
   my $sth = $dbh->prepare( $query );
   $sth->execute();
   my $ct = 0;
   while (my $tmp_href = $sth->fetchrow_hashref) {
      $ct++;
      $results{$ct} = $tmp_href;
   }
   %{ $href } = %results;
   ## also tried Storable's dclone(), but same results
   ## $href = dclone(\%results);
   print Dumper($href); ## prints desired results
}
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The resulting structure looks like this (it's exactly the way I want it): <code> $VAR1 = { '1' => { 'f1' => undef, 'f2' => 'bleep@hotmail.com', 'f3' => 'OTH', 'f4' => 'N',

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