Are there any debugger functions?

[frame via Digitalmars-d-debugger]

If a pointer has an invalid target a debugger in VS shows the 
error

`D0001: Error: Expression couldn't be evaluated`
when I try to access it.

Is there a debugger function to trigger this access which can be 
used inside an invariant?
I can assert it by checking if the pointer address is far to low, 
but this doesn't always work.