Take a common example of using the cache:

DataSet MyData = Cache["MyData"];
if(MyData == null){
 MyData = new MyDataSet();
 SomeAdapter.Fill(MyData); // Lengthy operation
 Cache["MyData"] = MyData;
}
// Do something with MyData

Now imagine this code executing simultaneously in two separate threads of
the same application. In both instances, the value in the Cache is null.
What goes where? Do two datasets get created/filled, but only one stored? Or
do two get stored - one in each separate context?

In other words, is there a possibility for multiple independant copies of
the Cache being created, or is the Cache truly global?