Debagging Parallel Nsight. How many GPU?

how many gpu is necessary for debagging program cuda on Parallel Nsight?
In the two requirements listed GPU. Both the GPU should support CUDA? Where will occur debug: on the GPU or CPU? Will it be a place to debug a program if the GPU will be the same (eg 2 GPU GTX570)?

The latest version of Nsight supports local debugging, meaning you will need just a single CUDA-capable card.
The debugging will take place on the GPU you choose with cudaSetDevice