  The strong CP problem is inseparably connected with the topology of gauge
fields and the mechanism of color confinement, which requires nonperturbative
tools to solve it. In this talk I present results of a recent lattice
investigation of QCD with the $\theta$ term in collaboration with Yoshifumi
Nakamura. The tool we are using to address the nonperturbative properties of
the theory is the gradient flow, which is a particular realization of momentum
space RG transformations. The novel result is that within QCD the vacuum angle
$\theta$ is renormalized, together with the strong coupling constant, and flows
to $\theta = 0$ in the infrared limit. This means that CP is conserved by the
strong interactions.
