Hey gedaiu,I'm still a novice to D, but here are some solutions I found. They can probably be improved.
1) Assigning to it an empty map https://ideone.com/h7ffmD 2) Removing all entries https://ideone.com/E7k2WLMy guess is that the first method is more efficient. I wish I knew how to do it without having to explicitly declare the "empty" variable.
Cheers.