I'm trying to render part of a (depth) cubemap to a separate (2D) texture, however the glsl 'textureCube'-function always returns 0.

Here's my frame buffer / texture generation code:
Code :
unsigned int size = 4096;
unsigned int frameBuffer;
glGenFramebuffers(1,&frameBuffer);
 
glBindFramebuffer(GL_FRAMEBUFFER,frameBuffer);
unsigned int texture;
glGenTextures(1,&texture);
 
glBindTexture(GL_TEXTURE_CUBE_MAP,texture);
glClearDepth(0.75);
for(int i=0;i<6;i++)
{
	glTexImage2D(GL_TEXTURE_CUBE_MAP_POSITIVE_X +i,0,GL_DEPTH_COMPONENT,size,size,0,GL_DEPTH_COMPONENT,GL_FLOAT,0);
	glFramebufferTexture2D(GL_FRAMEBUFFER,GL_DEPTH_ATTACHMENT,GL_TEXTURE_CUBE_MAP_POSITIVE_X +i,texture,0);
 
	glClear(GL_DEPTH_BUFFER_BIT);
}
glClearDepth(1.f);
glTexParameteri(GL_TEXTURE_CUBE_MAP,GL_DEPTH_TEXTURE_MODE,GL_LUMINANCE);
glTexParameteri(GL_TEXTURE_CUBE_MAP,GL_TEXTURE_COMPARE_FUNC,GL_LEQUAL);
glTexParameteri(GL_TEXTURE_CUBE_MAP,GL_TEXTURE_COMPARE_MODE,GL_COMPARE_R_TO_TEXTURE);
 
glDrawBuffer(GL_NONE);
glReadBuffer(GL_NONE);
bool valid = false;
if(glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
	valid = false;
else valid = true;
if(valid == true)
{
	unsigned char *pixels = new unsigned char[size *size];
	glReadPixels(0,0,size,size,GL_DEPTH_COMPONENT,GL_UNSIGNED_BYTE,&pixels[0]);
	for(unsigned int i=1243;i<1495;i++) // Read out some random pixels to make sure the previous code is working
		std::cout<<unsigned int(pixels[i])<<std::endl; // Prints out '191' for each pixel
	delete[] pixels;
}
 
glBindFramebuffer(GL_FRAMEBUFFER,0);
glBindTexture(GL_TEXTURE_CUBE_MAP,0);

The fragment shader:
Code :
#version 330 core
 
in vec2 UV;
 
out vec4 color;
 
uniform samplerCube depthTexture;
 
void main()
{
	float uvx = UV.x *2.0;
	float uvy = UV.y *2.0;
	float z = uvx -1.0;
	float y = uvy -1.0;
	float depth = textureCube(depthTexture,vec3(1.0,-y,z)).x;
	color.r = depth;
	color.g = depth;
	color.b = depth;
	color.a = 1;
}
'depth' is always 0.

Binding the cubemap to the shader location + the actual rendering to a screen quad:
Code :
glUseProgram(shader);
unsigned int locTexture = glGetUniformLocation(shader,"depthTexture");
 
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_CUBE_MAP,texture); // Same texture as generated earlier
 
glUniform1i(locTexture,0);
 
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER,vertexBuffer); // Two triangles with the vertices for a quad
glVertexAttribPointer(
	0,
	3,
	GL_FLOAT,
	GL_FALSE,
	(void*)0,
	0
);
glDrawArrays(GL_TRIANGLES,0,6);
OpenGL::DisableVertexAttribArray(0);

glGetError() reports no errors, what am I missing?