var x0 = d3.scale.linear().domain(…).range(…), // initial scale
    x = x0.copy(); // copy to use for axes and zoom behaviour

setInterval(function() {
  var translate = zoom.translate(),
      scale = zoom.scale(),
      xd = x0.domain(),
      dx = 1;

  // Set a new x-domain: offset by dx.
  x0.domain([xd[0] += dx, xd[1] += dx]);

  // Set the zoom x-domain (this resets the domain at zoom scale=1).
  zoom.x(x.domain(xd));

  // Reset the domain relative to the current zoom offsets.
  x.domain(x0.range().map(function(x) {
    return (x - translate[0]) / scale;
  }).map(x0.invert));
}, 1e3);