  The recent discovery of merging black holes suggests that a stochastic
gravitational-wave background is within reach of the advanced detector network
operating at design sensitivity. However, correlated magnetic noise from
Schumann resonances threatens to contaminate observation of a stochastic
background. In this paper, we report on the first effort to eliminate
intercontinental correlated noise from Schumann resonances using Wiener
filtering. Using magnetometers as proxies for gravitational-wave detectors, we
demonstrate as much as a factor of two reduction in the coherence between
magnetometers on different continents. While much work remains to be done, our
results constitute a proof-of-principle and motivate follow-up studies with a
dedicated array of magnetometers.
