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As the other answers already pointed out, there's no such spheric region. The field produced by the magnetic dipole will be given by $$\mathbf{B}_d(r,\theta)=\frac{\mu_0m_0}{4\pi}\frac{3\hat{\mathbf{r}}\cos\theta-\hat{\mathbf{z}}}{r^3}$$ So, adding both fields, we cannot make it null for a fixed $r$, since the component on the $z$ direction will be constant but the radial is $\theta$ dependent. What can be made, as @mcodesmart posted is to get a zero flux on a sphere. In this case, the radial field will be zero. For this we must have $$\frac{\mu_0m_0}{4\pi}\frac{3\cos\theta-\cos\theta}{r^3}+B_0\cos \theta=0\implies\\ r=\left(-\frac{\mu_0m_0}{2\pi B_0}\right)^{1/3}$$ which shows that the uniform field must be oriented in the opposite sense of the dipole.