I don't see a motivating testcase, and the description is bogus.

perl -e'$_="x";%h=map{$_=>1}(0..3);print $_' => x # global $_ is restored

perl -e'sub x{$_="ouch"};$_="x";%h=map{$_=>x}(0..9);print $_' => x # global $_ is restored

Do you just need a map with a lexical iteration variable other than $_?
$_ is properly restored.

Something like map sub($i){$i => 1} @array for nested maps?