You need as many bind variables as you have values. Try the following (untested):

my $bindvars = join(",", ("?") x scalar @values);
my $sql = <<END_SQL;
SELECT COUNT(*)
FROM some_table
WHERE some_column IN ($bindvars)
END_SQL

my $sth = $dbh->prepare_cached($sql) || die;
$sth->execute(@values) || die;
...
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