Best way to clear a PHP array’s values

Which is more efficient for clearing all values in an array? The first one would require me to use that function each time in the loop of the second example.

foreach ($array as $i => $value) {
    unset($array[$i]);
}

Or this

foreach($blah_blah as $blah) {
    $foo = array();
    //do something
    $foo = null;
}