You can re-initialize the array to be empty:

1. Foo[] myArray; //Define
   
2. 
   
3. //Do stuff
4. 
   
5. myArray = new Foo[0]; //Kills everything, call as many times as necessary
   

Besides attributing a brand new memory block allocation, like calsign's, a simple myArray = null; also works!
Another trick is if myArray was declared within a method or curly braces, that is, as a local variable,
it ceases to exist anyways after it gets outta scope!