It may be that local doesn't do what you think it does. It would make a lot more sense to write something like this:

package blarg;
use strict;
use warnings;

sub hrmph {
    our $global = "blarg";
    print "$global\n";
    local $global; 
    $global = "hrm, just in here!";
    print "$global\n";
    # when this scope is done, global goes back to "blarg" automatical
+ly
}
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Note that use vars is pretty much the same thing as our except that the package variable isn't bound locally to a sub as a pseudo-lexical. But if it was a case of use vars local would work the same way. It doesn't make the variable lexical, it makes the values you use in it local to the scope.