destroying a singleton object

Question

What is the best way to destroy a singleton object?

case A: Single threaded Environment
case B: Multi Threaded Environment

Sample snippets(if any) will be really helpful.

[EDIT] I don't have a specific use case I am just trying to understand that IF AT ALL the singleton has to be used how to destroy it correctly. As i understand, from the comments, there are 2 scenarios possible:
1. Destroy the singleton when no code is accessing it.(use smart pointers which will take care of destroying the object by itself using RAII)
2. Destroy a singleton when exiting the program irrespective of whether or not some code was holding on to the singleton. (explicitly destroy by deleting the instance just before main exits)

Answer 1

Don't create it in the first place!

Seriously, I strongly recommend you reconsider your choice of singleton, especially in a multithreaded environment. Instead just create an instance in main() and pass it down the call hierarchy to where it is needed.

You can use something like shared_ptr to ensure that the object stays around until no-one needs it any more.