First of all, I must confess that my knowledge of Physics is rudimentary (high-school level). So, the question I am going to ask may not be make much sense, and I apologize in advance if this is the case.
Question: Are there objects that can block graviational waves just as matter blocks light and produces a shadow? That is, a body in the shadow will not be able to detect any gravitational force due to the body that is being blocked.
A related question then will be: can there be places where there can be no gravity at all?
I did some search on the Internet which came up with references to Lesage's theory, a book on the discovery of gravitational waves, and a similar question at http://van.physics.illinois.edu/qa/listing.php?id=42143 though the answer to this last question seems to talk about shadows of light rather than that of gravity.