$ perl -le'
   use Encode qw( encode is_utf8 );
   my $x = "\xC9ric";
   print is_utf8(encode("iso-8859-1", $x))?1:0;
'
0

$ perl -le'
   use Encode qw( encode is_utf8 );
   my $x = "\xC9ric";
   print is_utf8(encode("UTF-8", $x))?1:0;
'
0