sub foo {
    ...

    ## get $ref back from bar()
    my($ref, %locations) = &bar($dbh);

    ...
  
    my $location_text = $locations{$ref->{'location'}};
}

sub bar {
    ...

    my $ref;
    while ($ref = $sth->fetchrow_hashref())
    {
        my $id = $ref->{'id'};
        my $location =  $ref->{'location'};
        $locations{$id} = $location;
    }

    $sth->finish;

    ## return $ref back to caller
    return $ref, %locations;
}